1. Field of the Invention
The invention relates to oil well tools. More particularly the invention relates to proper placement of a guide stock in a wellbore for diverting tools into a lateral borehole.
2. Prior Art
When a lateral borehole is to be drilled a certain sequence of events is known and practiced regularly. First a packer is set within a primary wellbore at a location downhole of the desired exit point for a lateral borehole. A whipstock is then run and inserted in the anchor, the whipstock having an orientation sub thereon which orients the face of the whipstock in the desired direction of the proposed lateral borehole. A drill is run and the lateral borehole created. The drill is removed, the whipstock is removed and a guide stock is stabbed into the original packer. Since the guide stock is provided with the same type of orientation sub it orients in the same direction that the whipstock originally did. This is an old and well-known sequence of events and would seem to indicate that the diverter face of the guide stock should be aligned with the lateral borehole. Unfortunately, however, during the kicking off of the drill from the whipstock, the whipstock tends to move due to the tremendous torque placed on the whipstock by the drill. Since the whipstock is in this (contorted to some degree) condition when the drill leaves the primary bore the exact angle and orientation of the window thereby created is somewhat different than planned. The movement does not translate to the packer and so when the whipstock is replaced by a guide stock for feeding other tools into the lateral borehole, it may not be aligned. The orientation of the guide stock, not having any torque loads thereon is that of what was originally planned and may not coincide with the actual orientation of the lateral borehole itself. For this reason it has always been challenging to properly orient the guide stock to align with the lateral borehole.
Prior art methods for aligning the guide stock include, as the most common and ubiquitous method, experience of the drill team. More specifically, upon removing the whipstock from the hole an inspection is made which to a skilled and experienced eye will indicate about how far off the planned orientation the lateral borehole has been drilled. This is accomplished by examining marks made on the whipstock by the drill bit such as how deep the marks are, where on the diverter face the marks are located, etc. These marks tell the experienced driller where the bit bound and kicked off the whipstock diverter face and thus in which direction drilling began. From these determinations the drill team will reorient the guide stock by attaching the orientation sub to the guide stock differently. This modifies the orientation of the diverter surface so as to be more likely to be aligned with the lateral borehole. While skill and experience are of the most important assets in making a well work, the guestimate method of placing a guidestock leaves exactness to be desired.